1. Field of the Invention
This invention relates to the erection of structures and more particularly it concerns novel techniques for the construction of offshore towers and platforms such as are used in exploration and recovery of resources such as oil from beneath the sea bed.
2. Description of the Prior Art
Offshore towers and platforms of the type to which the present invention pertains are shown in U.S. Pat. No. 3,857,247 to Lindsey J. Phares and in U.S. Pat. No. 3,876,181 to Joseph E. Lucas. In both these patents there is described a two component system comprising a template or tower and a platform or deck, which are separately floated or carried by barge out to a desired offshore location. When the template arrives on location it is affixed in upright or vertical position to the sea bed with its legs extending up well beyond the water surface. The deck or platform is then positioned between the tower legs and is jacked up along the legs so that it is clear of the water surface and of all wave action. The platform is then pinned to the template and drilling and production operations are then carried out from the stably mounted, elevated platform.
Both the Phares and Lucas patents show arrangements for mounting jacking tubes to be suspended from the upper ends of the template legs so they extend down alongside the legs to the platform. Jacking mechanisms are provided on the platform to grip the jacking legs and pull the platform up via the jacking legs to the top of the template legs. After the elevated platform is secured to the template the jacks and jacking legs may be removed for use in the erection of another offshore tower.